onnxruntime

Softmax interface update (#12469)

* Template datatype for SoftmaxWithRawMaskSmallKernel in ROCm EP

* Remove valid_items usage from SoftmaxWithRawMaskSmallKernel for ROCm EP

The kernel already masks off invalid items and this gives a much
faster implementation in hipCUB.

* Update accumulator type in ROCm EP for SoftmaxWithRawMaskSmallKernel

Hard code accumulator to fp32 for hipCUB in indicated kernel.

* Reset casting to old behavior

* Document steps to optimize SoftMax kernel on ROCm EP

Usage of the hipCUB valid_items interface on reduction operations
has a significant performance impact. Masking all thread data to
avoid need to use the valid_items interface to hipCUB.